Processing copper base alloys

ABSTRACT

A process for obtaining improved strength properties and improved stress corrosion resistance in copper base alloys including the steps of hot rolling, annealing, cold rolling, and stress relief annealing.

O United States Patent 1191 1111 3,816,187 Smith et al. June 11, 1974[54] PROCESSING COPPER BASE ALLOYS 2.101.087 12/1937 Munson 1. 75/15752.3 .208 2 9 4 t .5 1 1 Rkhard Dale 81111115111111 1.122.095 851921fic'h'il fl... 1 121157.? Rd-1Madisomconn- O6443;Irwi" 7.663.311 5/1972Chin etal. 148/115 R Broverman, 7337/8 S. Shore Dr., A t. 1017, Ch'.111. 60649 p FOREIGN PATENTS OR APPLICATIONS [22] Fledi July 1972578.873 7/1946 Great Britain 75/1575 [21] Appl. No.: 274,807

7 Related Application Data Primary Examiner-W. W. Stallard [60] Divisionof Ser. No. 115,839, Feb. l6 1971. Anomey, Agent, or Fi,m RObert Bachmanabandoned which is a continuation of Ser. No. 800,354, Feb l() 1969,abandoned, which is a continuation of Ser. No. 530,942, March 1, 1966,

b d d.

a 57 ABSTRACT 52 us. c1 l48/ll.5 R

[51] Int. Cl. C22f l/08 A process for obtaining improved strengthproperties [58] Field of Search l48/1l.5 R, 12.7 and improved stresscorrosion resistance in copper base alloys including the steps of hotrolling, anneal- [56] References Cited ing, c0ld rolling, and stressrelief annealing.

UNITED STATES PATENTS 8/1935 Price 75/1575 3 Claims, 2 Drawing FiguresPATENTEnJun 1 1 m4 CROSS REFERENCE TO RELATED APPLICATIONS Thisapplication is a division of application Ser. No. 115,839, filed Feb.16, 1971, by Richard Dale Smith and lrwin Broverrnan for Copper BaseAlloys, now abandoned, which in turn is a Continuation of applicationSer. No. 800,354, filed Feb. 10, 1969, by Richard Dale Smith and lrwinBroverman for Copper Base Alloys," now abandoned, which in turn is aContinuation ofapplication Ser. No. 530,942, filed Mar. 1, 1966, byRichard Dale Smith and lrwin Broverman for Copper Base Alloys, nowabandoned.

The present application relates to new and improved copper base alloys.More particularly, the present invention resides in greatly improvedcopper base alloys containing zinc, aluminum and nickel, said alloyshaving greatly improved physical properties and being suitable for awide range of applications, including castings, forgings, extrusions,and hot or cold rolled or drawn products. The improved alloys of thepresent invention are particularly suitable for use in wrought products.

Over the years, numerous attempts have been made to improve the strengthcharacteristics of ductile brass withoutsacrifice of formability. Theseattempts have concentrated on utilizing a great variety of alloyingadditions in order to achieve this goal. Some of these alloyingadditions are quite expensive and add considerably to the-cost of thealloy.

in addition, the art has thoroughly explored manyunusualthermo-mechanical processesin order to improve the strengthcharacteristics without sacrificing formability.

The high strength brasses which have been developed in the art generallyare multiphase alloys having limited ductility and cold formability.Such alloys are most suitable for application as castings or hot workedproducts.

Despite these extensive investigations, 70/30 brass has prevailed overthe years as the best and most economical copper base alloy for severeforming applications.

Accordingly, it is a principal object of the present invention toprovide an improved copper base alloy.

It is an additional object of the present invention to provide a copperbase alloy having improved strength levels in either the fully annealedor cold workedtempers.

It is an additional object of the present invention to provide improvedcopper base alloys as aforesaid which achieve improved strengthcharacteristics with minimal sacrifice in formability.

It is an additional object of the present invention to provide animproved copper base alloy as aforesaid, said alloy being characterizedby relatively low cost so that it is economically suitable on a largescale.

Further objects and advantages of the present invention will appearhereinafter.

In accordance with the present invention, it has now been found that-theforegoing objects may be readily and conveniently achieved. The improvedalloy of the present invention consists essentially of the followingingredients in the following ranges, wherein all percentages are weightpercentages: copper from'66 to 80.0

percent, zinc from 15.0 to 32.5 percent, aluminum from 1.5 to 5.0percent, and nickel from 0.2 to 5 percent.

It has been found that the foregoing alloy achieves greatly improvedphysical properties with minimal sac range of 50,000 to 75,000 psi.

In addition, and importantly the alloys of the present invention arecharacterized by a high formability. Using the highly formable /30 brassas a standard, the alloys of the present invention have comparableformability. This is particularly surprising in view of the highstrength of the alloys of the present invention.

These surprising characteristics .in an inexpensive alloy areparticularly unexpected in view of the extensive art in this fieldattempting to approximate these characteristics.

The alloys of the present invention are known as modifiedaluminum-brasses and basically have either of the following structures:(1) an alpha (face-centered cubic) structure; or (2) an alpha plus alimited amount of beta (body-centered cubic) structure.

The addition of aluminum to copper-zinc alloys has long been known forits strengthening effect on such alloys. The disadvantage of thealuminum addition is that in saturated alpha phase alloys, which havehighest strengths, small variation in aluminum content generally resultsin large variations in ductility and strength. These large variationsare a result of the structure of the saturated alloy changing markedlywith aluminum content. For example a change in aluminum content of onepercent may cause an increasein beta phase content of up to 33 percent.

In accordance with the present invention it has been surprisingly foundthat the addition of nickel in the range of 0.2 to 5 percent by weightovercomes the disadvantages of the ternary copper-aluminum-zinc alloyssuch that properties and structure are more uniform over a practicalrange of aluminum content. In addition, a very marked grain refiningeffect occurs upon the addition of nickel, which is highly advantageous.

In accordance with the present invention the alloying ingredients mustcritically fall within the foregoing ranges. The copper content mustfall within the range of 66 to percent by weight and preferably from 70to 76 percent by weight. Below 66 percent by weight the strength fallsoff markedly and above 76 percent by weight in saturated alloys anadditional phase, termed gamma-having a complex cubic crystal structure,may be encountered which limits the ductility of the alloy.

Similarly, the zinc content is within the range of 15.0 to 32.5 percentby weight and preferably from 21 to 28 percent. The aluminum contentshould be maintained in the range from 1.5 to 5.0 percent by weight andpreferably 2.5 to 4.5 percent and the nickel content should bemaintained in the range 0.2 to 5 percent and preferably 0.4 to 2.0percent.

For maximum ductility-formability at any given copper-aluminum level,the nickel content should be betweenv 0.2 and'l.0 percent while forgreater strength and lesser ductility the nickel may approach higherlevels up to 5 percent. At higher nickel levels ductility is reduced tosuch an extent that usefulness as a wrought product isimpaired.

In general, the lower nickel content alloys are high strength, highductility materials; whereas the higher nickel content alloys provideeven higher strengths, but lower ductility.

The composition of specific alloys within the above ranges are subjectto the further internal restriction that at about the 71.5 percent levelof copper the aluminum content should preferably be in the range of 1.5

to 4.0 percent in order to insure high ductility-strengthcharacteristics and at about the 74 percent level of copper the aluminumcontent should preferably be between 2.5 and 5.0 percent for the samereasons. Proportionate adjustments of aluminum content for the variouscopper contents between the specified limits should preferably be made.

Furthermore, in order to attain the preferred properties the aluminumcontent should preferably be related to the zinc content in accordancewith the following equation:

Weight %'AI 0.30 wt% Zn 10.3 i 1.25 The subject alloys are representedin the attached I drawings which are isothermal (932F), constant nickel(0.5%) sections of the quaternary phase diagram. FIG. I shows therelative location of the alloys of the present invention on the ternaryphase diagram. FIG. 2 shows the shaded section of FIG. 1. In FIGS. 1 and2 the solid line represents the alpha phase boundary. In FIG. 2, thedotted line represents the alloys of the present invention at constant0.5 percent nickel. Similar diagrams may be readily constructed forother nickel levels.

The structure of the alloys of the present invention in the cold workedand annealed condition is either l) a matrix of fine grained,face-centered cubic, alpha phase (saturated or very nearly so), or. (2)saturated alpha plus beta phase, with both structure l) and structure(2) having very fine intermetallic compound and/or precipitate particlesdispersed throughout.

The alloys of the present invention may include in addition to theforegoing materials conventional impurities typically found incommercial copper base alloys. In addition, various other alloyingingredients may be added to achieve particularly desirable results.Common impurities may include: lead; tin; phosphorus; iron; manganese;and silicon. Forminimizing dezincification in corrosive environments,the addition of arsenic, antimony or phosphorus may be desirable in an.

amount from 0.02 to 0.10 percent.

In general, the alloys of the present invention have an alpha plusparticulate phase or an alpha plus beta plus particulate phase structureand are utilizable in a wide variety of applications. In view of theirhigh strength and high formability, they are preferably provided in thewrought form. The oxidation resistance and castability of the alloys ofthe present invention are excellent suggesting wide spread applicationas high strength, low cost foundry alloys while their excellent hotforming properties also make them desirable for forgings as well asextrusions. In general, better combinations of mechanical properties atlow costs are obtainable with the alloys of the present invention thanare available in any currently produced. copper base alloys regardlessof price.

Processing of the subject alloys requires no unusual treatment. As anexample, the processing to sheet is as follows. Melting and casting areperformed under similar conditions as brass alloys. Direct chill (DC)casting is particularly suitable. Hot rolling is easily accomplishedusing normal brass mill procedures. Under rapid coolingconditions anon-equilibrium structure may be obtained which reduces initial coldrollability. This may be overcome by an anneal in the range of lO0O tol200F wherein practically equilibrium proportions of alpha and betaphases are attained.

It has been observed in the processing of the subject alloys that theyexhibit an unusually high response to low temperature stress reliefannealing following cold working. Normally, copper base alloys whichhave been heavily cold worked may respond with an increase in yieldstrength of up to 15v percent when annealed at temperatures below therecrystallization temperature. This increase also normally is ofpractical consequence only within a relatively narrow range of annealingtemperatures (50 to' F). In the alloys of this invention, increases inyield strength of 30 to 40 percent have been noted upon low temperatureannealing of material cold rolled 50 percent. Further, this responseoccurs over a wider range of temperature 1 50 to 200F span), therebyincreasing its commercial applicability. The magnitude of improvement instrength properties will be illustrated in the examples which form apart of the present specification.

A further outstanding characteristic of the subject alloys is a verymarked improvement in stress corrosion resistance. The copper-zincbrasses are highly susceptible to stress corrosion'cracking when exposedto certain corrosive environments; This susceptibility is proportionalto zinc content and hence alloys containing more than 15% zinc arerarely chosen for stressed applications in corrosive environments. Ithas been found that the nickel modified aluminum brasses have greatlyimproved resistance to stress corrosion cracking when compared with thebinary copper-zinc alloys. This behavior will be apparent'from theensuing examples. Coupled with this stress corrosion resistance is ahigh level of resistance to general corrosion.

The present invention will be more readily understandable from aconsideration of the following illustrative examples.

EXAMPLE I Alloys having the compositions listed below were prepared fromcathode copper, slab zinc, nickel metal, and aluminum metal pellets.Preparation followed the ensuing sequence. Cathode copper chunks andnickel chunks were melted under charcoal, the desired aluminum contentwas added and stirred in, zinc chunks Table [11 Alloy Limiting DrawRatio Olsen Bulge Height 11 2.240 0.380" 1V 2.225 0.370" V 2.225 0.391"V1 2.260 0.420"

EXAMPLE IV Resistance to stress corrosion cracking is of importance inmany applications. The improved alloys of the present invention havedemonstrated a marked superiority over common brasses in-this respect.In an accel- Table I Alloy Composition Cold Rolled 50% An Hit H wt YieldYield Percent Yield Yield Percent Strength Strength Elongation StrengthStrength Elongation psi psi psi psi 1 75.9Cu 19.4Zn 4.0Al 0.7Ni 95,500124,000 1.7 49,500 79,000 38 ll 74.2Cu 21.8Zn 3.5Al 0.5Ni 86,000 125,0002.0 49,000 78,000 36.5 111 71.3Cu 21.7Zn 4.0Al 3.0Ni 91,000 128,000 2.062,000 89,000 26 1V 72.0Cu 25.0Zn 2.5Al 0.5Ni 91,000 122,000 3.0 53,00083,000 34 V 76Cu Zn 4A1 89,000 1 14,000 2.0 27,000 65,000 57 *41,00072,000 39 V1 70Cu Zn 74,500 90,000 Y 3.5 *2l,800 53,000

' Annealed at 800F EXAMPLE 11 Alloy V from Example [was given thefollowing erated test in a solution containing (Nl-1 (SO.,), Cu(- S0 andNH OH, highly stressed strip samples retreatment after the final coldroll: 1 hour anneal at 30 375F. The properties were as follows:

Table IV Alloy Time to Failure in Atmosphere Time to Failure inAccelerated Test or Amount of relaxation in 500 Hrs.

(70/ 30 brass) 85/15 brass 14% relaxation 500 hrs. 43% relaxation 500hrs. complete failure 4 hrs.

No failures at 4 mos. no failures at 10 mos. 8 to 15 weeks completefailure 48-72 hrs. no failures at 12 mos.

Table 11 Cold Rolled 5071 Cold Rolled 50% 1 hour at 375F Yield Strength91,000 psi 114,500 psi Tensile Strength 128,000 psi 132,000 psiElongation 2.0% 1.2%

EXAMPLE 111 Several of the alloys prepared in Example I were evaluatedfor formability using two common measurements, i.e., limiting draw ratiodetermination for evaluating deep drawability, and Olsen cup testing tocheck This invention may be embodied in other forms or carried out inother ways without departing from the spirit or essentialcharacteristics thereof. The present embodiment is therefore to beconsidered as in all respects illustrative and not restrictive, thescope of the invention being indicated by the appended claims, and allchanges which some within the meaning and range of equivalency areintended to be embraced therein.

What is claimed is:

l. A process for obtaining improved strength properties and improvedstress corrosion resistance in copper base alloys consisting essentiallyof copper from 66 to 76 percent by weight, zinc from 15.0 to 32.5percent by weight, aluminum from 2.5 to 4.5 percent by weight and nickelfrom 0.2 to 5.0 percent by weight, consisting essentially of the stepsof:

B. annealing said alloy at a temperature of from 'l000 to 1200F;

group consisting of arsenic, phosphorus and antimony in an amount from0.02 to 0.10 percent by weight.

'3. A process according to claim 1 wherein said material is stressrelief annealed at a temperature of 375F for one hour.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 7Dated June 11, 197 1 Inventor(5) Richard Dale Smith and Irwin BrovermanIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:-

In the heading, aft er "Richard Dale Smith, 51 Twin Cones Rd. Madison,Conn. 06 4 13; Irwin Broverman, 7337/B 1017, Chicago, Ill. 606 19"insert 8'. Shore Dr. vApIz. ---assignors to Olin Mathieson ChemicalCorporation, a

corporation of Virginia---.

Signed and sealed this 29th day of October 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Commissioner of Patents AttestingOfficer USCOMM-DC 60376-P69 n uis. GOVERNMENT PRINTING OFFICE I9590366-33l F ORM PC3-1050 (1069)

2. A process according to claim 1 wherein said copper base alloycontains a material selected from thE group consisting of arsenic,phosphorus and antimony in an amount from 0.02 to 0.10 percent byweight.
 3. A process according to claim 1 wherein said material isstress relief annealed at a temperature of 375*F for one hour.